Upload
vankhanh
View
219
Download
0
Embed Size (px)
Citation preview
1
General Chemistry
8 LECTURE COURSEDr. Wolfgang Schmitt
Room 2.03, SNIAMS Building
E-mail: [email protected]
further text books:
Chemistry- the molecular nature of matter and change – Silberberg 3rd
edition
Chemistry-molecules, matter and change - Atkins and Jones, 5th edition
WebSites: http://www.tcd.ie/Chemistry/teaching/chemistry/jf/intro/intro.php
http://now.brookscole.com/kotz6e
Recommended Book: Chemistry and Chemical Reactivity - J.C. Kotz, P.M. Treichel, G.C. Weaver 6th edition, Thomson Books/Cole
Lecture 1
1.1 Why do we study Chemistry?
1.2 Classifications of Matter
1.3 Properties of Matter
1.4 Mixtures
Outline
2.1 SI Units
2.2 Derived units
2.3 Scientific Notation
2
Why Chemistry ???
Experimental setup: A flowerpot with a single drainage hole is filled with a mixture
of iron oxide (Fe2O3) and coarsely ground aluminum (reaction mixture: Thermit®
mixture). This is covered with a mixture of magnesium and barium peroxide (BaO2) (ignition mixture). A strip of magnesium serves as a wick. A porcelain dish filled with sand is placed underneath.
3
The magnesium-barium peroxide mixture is ignited by the burning magnesium ribbon.
Magnesium oxide and barium oxide are produced in a strongly exothermic reaction according to:
BaO2 + Mg BaO + MgO
The heat emitted by this reaction ignites the Thermite® mixture.
The Thermite Reaction
Due to very high temperatures (up to 2400°C, reaction enthalpy: 852 kJ/mol) the reaction of iron oxide with aluminium forms elemental iron, which seeps in liquid form out of the
flower pot drainage hole:
Fe2O3 + 2 Al 2 Fe + Al2O3
The molten iron is collected in the porcelain dish where it immediately hardens. An afterglow can be clearly seen. The Thermite® process is used to weld and join iron parts (such as iron tracks and street car tracks). A number of other metals can be obtained from
their oxides by reduction with aluminium.
Indices Coefficients
Exothermic : Heat is released during this reaction (↔ endothermic)
CHEMISTRY
Is the study of matter,
its properties,
the changes that matter undergoes,
and
the energy associated with these changes.
4
Chemical Systems
…… the substance viewed as a “chemical system”
chemical system entities of the system
Construction; Synthesis
Sub-division; Analysis
Nature of the building units: Atoms, Molecules, Ions
Number of building units
Arrangement of the building units
quantitative aspects
qualitative aspects
structure
●
●
●
The Physical States of Matter
5
A Gas has neither a definite shape nor
definite volume:
it adopts the volume and shape of the vessel
containing it.
A Liquid has definite volume but not shape:
it adopts the shape of the vessel containing it.
A Solid has definite volume and shape:
which is independent of the vessel containing it.
Short- and long-range order
Short range order
Changes of State
Solid
Liquid
Gas
Vaporisation/Boiling
Condensation
Melting Fusion/Freezing
RequiresEnergy
LiberatesEnergy
6
Definitions
Chemical Propertiesthose which the substance shows
as it interacts with, or transforms
into, other substances, such as:
flammability, corrosiveness
Matter anything that has mass and volume -the “stuff” of the
universe
Composition the types and amounts of simpler substances that
make up a sample of matter
Properties the characteristics that give each substance a unique
identity
Physical Propertiesthose which the substance
shows by itself without interacting
with another substance, such as:
colour, melting point, boiling
point, density
Sample Problem Distinguishing Between Physical and Chemical Change
PROBLEM: Decide whether each of the following process is primarily a physical or a chemical change, and explain briefly.
Criteria: “Does the substance change composition or just change form?”
SOLUTION:
(a) Frost forms as the temperature drops on a humid winter night.
(b) A cornstalk grows from a seed that is watered and fertilized.
(c) Dynamite explodes to form a mixture of gases.
(d) Perspiration evaporates when you relax after jogging.
(e) A silver fork tarnishes in air.
(a) physical change (b) chemical change (c) chemical change
(d) physical change (e) chemical change
7
An Extensive property is dependent on the extent of the sample
An Intensive property is independent of the extent of the sample
Temperature, Melting point, Density
Mass, Volume, Length
Intensive properties help identify a particular kind of matter
Extensive properties relate to the amount of matter present
Distinguishing between Intensive and Extensive Properties
●
●
●
●
Examples: water, ammonia, sucrose, gold, oxygen
A Substance is a form of matter that has a definite composition and distinct properties.
It is important to distinguish between two different kinds of matter –i.e. Pure Substance and Mixtures:
Pure substances have:
Fixed and definite composition
Fixed and definite properties
Their components cannot be separated by simple physical means
Pure Substances and Mixtures
●
●
●
8
A mixture is a combination of two or more substances in which
the substances retain their distinct identities.
1. Homogenous mixture – composition of the mixture is the same
throughout.
2. Heterogeneous mixture – composition is not uniform throughout.
soft drink, solder
cement, iron filings in sand with a magnet
Mixtures
Can easily be separated by
physical means
Solutions : A homogeneous mixture is also called a solution.
Solutions in water are called aqueous solutions, and arevery important in chemistry. Although we normally thinkof solutions as liquids, they can exist in all three physical
states.
9
Chemical Analysis
• Filtration:
Separates components of a mixture based upon differences in particle
size.
• Distillation:
Separation is based upon differences in volatility.
• Chromatography:
Separation is based upon differences in solubility in a solvent versus a chemical affinity to a stationary phase.
• Crystallisation:
Separation is based upon differences in solubility of components in a mixture.
……… often uses physical techniques
Methods for separating the components of mixtures:
Classification of Matter
10
Measurement Measurement –– SI UnitsSI Units
SI - Base Units
Physical Quantity Unit Name Abbreviation
mass
metre
kg
length
kilogram
m
time second s
temperature kelvin K
electric current ampere A
amount of substance mole mol
luminous intensity candela cd
11
Common Decimal Prefixes Used with SI Units
Prefix Prefix Symbol
Number Word Exponential Notation
tera T 1,000,000,000,000 trillion 1012 giga G 1,000,000,000 billion 10
9
mega M 1,000,000 million 106 kilo k 1,000 thousand 103
hecto h 100 hundred 102 deka da 10 ten 10
1
----- ---- 1 one 100 deci d 0.1 tenth 10-1 centi c 0.01 hundredth 10-2 milli m 0.001 thousandth 10-3
micro µ 0.000001 millionth 10-6
nano n 0.000000001 billionth 10-9 pico p 0.000000000001 trillionth 10-12
femto f 0.000000000000001 quadrillionth 10-15
Derived SI Units
Quantity Definition of Quantity SI unit
Area Length squared m2
Volume Length cubed m3
Density Mass per unit volume kg/m3
Speed Distance traveled per unit time m/s
Acceleration Speed changed per unit time m/s2
Force Mass times acceleration of object kg * m/s2
( = newton, N)
Pressure Force per unit area kg/(ms2)
( = pascal, Pa)
Energy Force times distance traveled kg * m2/s2
( = joule, J)
12
Volume
… SI derived unit for volume is cubic metre (m3)
1 cm3 = (1 x 10-2 m)3 = 1 x 10-6 m3
1 L = 1000 mL = 1000 cm3 = 1 dm3
1 mL = 1 cm3
1 dm = 10 cm
1 dm3 = 10cm x 10cm x 10cm = 1000 cm3
Density……… SI derived unit for density is kg/m3
1 g/cm3 = 1 g/mL = 1000 kg/m3
density = mass
volumed =
mV
A piece of platinum metal with a density of 21.5 g/cm3 has a volume of
4.49 cm3. What is its mass?
d =mV
m = d x V
= 21.5 g/cm3 x 4.49 cm3 = 96.5 g
13
Temperature …… Scales and Interconversions
Kelvin (K) - The “absolute temperature scale” begins at absolute zero
and only has positive values.
Celsius (oC) - The centigrade temperature scale is the most commonly
used scale around the world, water freezes at 0oC, and boils at 100oC.
T (K) = T (oC) + 273.15 T (oC) = T (K) – 273.15
….. In science
0oC = 273.15Kabsolute zero = – 273.15oC